Crosshatched designs similar to the
drawing have been found engraved on
shells at the site, Henshilwood says. So
the patterns may have held some sort
of meaning for their makers. But it’s
hard to know whether the crossed lines
represent an abstract idea or a real-life
concern. Some modern hunter-gatherer
societies create abstract-looking designs
that actually depict animals, objects or
people, he says.

Whatever the drawing’s original
significance, it shows that Stone Age

BODY & BRAINSuperbugs’ new foe has sneaky tacticsAntibiotic uses a novel way to get around bacteria’s defenses

BY LAUREL HAMERS

Drug-resistant bacteria have a new challenger. A new molecule can kill deadly
strains of common bacteria, such as

Klebsiella pneumonia and Escherichia
coli, that are resistant to most existing
antibiotics. The potential drug works
differently from currently available antibiotics, which may make it harder for
bacteria to develop resistance, researchers report in the Sept. 13 Nature.

Most antibiotics kill bacteria by weak-ening their cell wall or by preventing theproduction of certain proteins. But overtime, bacteria have evolved ways to cir-cumvent these drugs. And as antibioticsare used frequently in both hospitals andagriculture, resistant bacterial strainsare becoming more common. Infectionswith multidrug-resistant microbes areparticularly worrisome, because thesesuperbugs can turn usually easy-to-treatillnesses like urinary tract infections orstrep throat into deadly ordeals.

The new molecule inhibits a key
enzyme in the cell membrane that
helps the bacteria secrete proteins.

“We’re hitting a new target,” says study
coauthor Peter Smith, an infectious disease researcher at Genentech, a biotech
company based in South San Francisco,
Calif. A new target means that strategies that bacteria use to evade existing
antibiotics won’t work here, giving the
molecule an edge.

When the enzyme is blocked, proteinsbuild up in the cell membrane until themembrane bursts, ultimately killing thebacterial cell, says Floyd Romesberg, achemist at the Scripps Research Institutein La Jolla, Calif., who wasn’t part of thestudy. Romesberg developed precursorspeople in southern Africa communi-cated something they considered impor-tant by applying crosshatched patternsto different surfaces, says archaeologistPaul Pettitt of Durham University inEngland. “If there is any point at whichone can say that symbolic activity hademerged in human society, this is it.”But archaeologist Maxime Aubertof Griffith University in Southport,Australia, isn’t so sure. Henshilwood’steam can’t exclude the possibility,for example, that the apparent draw-ing resulted accidentally from peoplesharpening the tips of pigment chunkson rocks to make Stone Age crayons,Aubert says.

Henshilwood disagrees. Experimental
reproductions of the crosshatched pigment pattern, drawn on rocks like those
at the South African cave, indicate that
the lines were intentionally produced and
were originally darker and better defined,
he says. Previous evidence also suggests
that ancient humans at the cave used pigment as a glue ingredient and possibly as
a sunscreen. But the experimental drawings produced too little powder to use
as a glue additive or a sunblock. Ancient
pigment wielders appear to have wanted
only to draw a design on the stone.

Henshilwood’s team has demonstrated how to identify deliberate drawings at ancient human sites by excluding
other possible explanations for making
pigment strokes, says archaeologist
Gerrit van den Bergh of the University
of Wollongong in Australia. “It is likely
that further evidence for early symbolic
behavior will be found in the very near
future.” s

to the antibiotic in his lab, but the new
version is more effective, he says.

In tests in cultured human cells and
in mice, the molecule killed off a variety
of common gram-negative bacteria that
cause infections in humans, including

E. coli and Pseudomonas aeruginosa,
and was also effective against gram-positive bacteria. Gram-negative bacteria, named because of how they appear
when stained for viewing under a
microscope, are notoriously difficult to
attack with antibiotics because of the
microbes’ hard-to-penetrate cell membrane (SN: 6/10/17, p. 8). The molecule
also destroyed bacterial strains that are
resistant to multiple kinds of antibiotics.

The molecule will need to go through
additional testing and tweaking before
it can be used in humans, Smith says.

And it’s not a permanent solution to
the growing problem of antibiotic resistance. Eventually, if molecules of this
type are widely used as antibiotics,
bacteria will evolve resistance, as they
always do. But for now, it’s a step ahead. s

The 73,000-year-old red marks on this stone from a South African cave are remnants of a

crosshatched design that may be the earliest known drawing. The inset shows what the larger
pattern would have looked like as it extended beyond the edges of the surviving piece of rock.